Some references from Beer's "Encyclopedia of Tibetan Symbols and Motifs":

p. 234:A single-pointed vajra represents both the central chan-nel as Mt Meru's central axis, and the union of all dualitysymbols conceived of as non-dual. These include wisdom andcompassion, emptiness and bliss, absolute and relative truths.

p. 239:The deity Kalachakra is described as wearing a long rosary ofsingle-pointed vajras, although iconographically Kala-chakra's rosary is more often depicted as a long chain offive-pronged vajras with a crossed vajra at its lower centre.

p. 284:The sharp point of Yamantaka's harpoon- which is de-scribed as a single-pointed vajra - symbolises penetrativeinsight ...

Through Dzogchen we can really understand what God is and we don’t have to worry if there is a God or not. God always exists as our real nature, the base, for everybody. - Chögyal Namkhai Norbu

In the Ngagrim Chenmo series, Lama Tsongkhapa stated in accordance with the Susiddhi Tantra that when doing mantra recitation during a Kriya practice, a wooden single-pronged vajra carved and blessed by the practitioner should be held in the right hand (if I'm remembering this correctly). While I have yet to see this in practise in the Tibetan tradition, I have a strong suspicion that the Shingon tradition maintains it.

Yeah, I've seen one=pronged dorjes at Shingon temples in Japan. However, recently, a Tibetan Teacher gave me one. So that's the reason for my original query. In four decades, I had not seen one of these in Tibetan Buddhism before.